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Tanaka K.,Hiroshima University | Takahashi Y.,Hiroshima University | Sakaguchi A.,Hiroshima University | Umeo M.,Hiroshima University | And 4 more authors.
Geochemical Journal | Year: 2012

Vertical profiles of iodine-131 and cesium-137 emitted from the Fukushima Daiichi Nuclear Power Station were determined in soil core samples collected in Fukushima prefecture. The profiles showed that more than 76% of the radionuclides were retained within 5 cm of the surface. Leaching experiments showed that cesium was strongly bound to soil particles which could not be leached with 2 M HCl, while more than 40% of iodine was incorporated into humic substances. © 2012 by The Geochemical Society of Japan. Source

Ohno T.,Gakushuin University | Muramatsu Y.,Gakushuin University | Miura Y.,Fukushima Prefecture Government | Oda K.,Gakushuin University | And 5 more authors.
Geochemical Journal | Year: 2012

In order to understand the behavior of radionuclides released from the Fukushima Daiichi nuclear power plant, the depth distributions of radiocesium and radioiodine were investigated in a wheat field, a rice paddy, an orchard, and a cedar forest in Koriyama, Fukushima Prefecture. Our results demonstrate that, following the nuclear power plant disaster, more than 90% of the radionuclides were distributed in the upper 6 cm of the soil column in the wheat field and within 4 cm of the surface in the rice paddy, orchard, and cedar forest. According to the measurement of radionuclides in the three adjacent agricultural fields, the variation of deposition densities in the wheat field was smaller than that of the orchard and rice paddy, suggesting that the low permeability of the orchard and paddy soils may cause horizontal migration of radionuclides during the initial deposition. This result indicates that the deposition densities in the wheat field should be appropriate for estimating the amount of fallout in the area. The deposition densities of 134Cs, 137Cs, and 131I in this area were estimated to be 512 ± 76 (SD, η = 5), 522 ± 80 (SD, η = 5), and 608 ± 79 (SD, η = 5) kBq/m2 (decay corrected to April 1, 2011), respectively. A comparison of the deposition density between the wheat field and the cedar forest suggests that more than half of the radionuclides are distributed in the tree canopies of the evergreen forestland. © 2012 by The Geochemical Society of Japan. Source

Parajuli D.,Japan National Institute of Advanced Industrial Science and Technology | Takahashi A.,Japan National Institute of Advanced Industrial Science and Technology | Tanaka H.,Japan National Institute of Advanced Industrial Science and Technology | Sato M.,Fukushima Agricultural Technology Center | And 3 more authors.
Journal of Environmental Radioactivity | Year: 2015

Cesium extraction behavior of brown forest type soil collected from paddy fields in Fukushima nuclear accident affected areas was studied. In nitric acid or sulfuric acid solutions at elevated temperature, the concentration of Cs in soil available for extraction, m0, has been estimated on the basis of modified canonical equation and the equations derived from assumed equilibria. With the variation in temperature, mixing time, and soil to solvent ratio, the observed m0 values in 0.5M acid solution ranged between 1.5 and 2.9mg cesium per kilogram of soil. By increasing the acid concentration to 3M, the value of m0 could be sharply increased to 5.1mg/kg even at 95°C. This variation in the extractable concentration of cesium with the parameters signifies the existence of different binding sites in the soil matrix. The results observed for uncontaminated sample could be reproduced with the radioactive cesium contaminated sample belonging to the same soil group. © 2014 Elsevier Ltd. Source

Fumoto T.,Japan National Institute for Agro - Environmental Sciences | Yanagihara T.,Hokkaido Kamikawa Agricultural Experiment Station | Saito T.,Fukushima Agricultural Technology Center | Yagi K.,Japan National Institute for Agro - Environmental Sciences
Global Change Biology | Year: 2010

Rice production is a substantial source of atmospheric CH4, which is second only to CO2 as a contributor to global warming. Since CH4 is produced in anaerobic soil environments, water management is expected to be a practical measure to mitigate CH4 emissions. In this study, we used a process-based biogeochemistry model (DNDC-Rice) to assess the CH4 mitigation potentials of alternative water regimes (AWR) for rice fields at a regional scale. Before regional application, we tested DNDC-Rice using site-scale data from three rice fields in Japan with different water regimes. The observed CH4 emissions were reduced by drainage of the fields, but were enhanced by organic amendments. DNDC-Rice gave acceptable predictions of variation in daily CH4 fluxes and seasonal CH4 emissions due to changes in the water regime. For regional application, we constructed a GIS database at a 1 × 1 km mesh scale that contained data on rice field area, soil properties, daily weather, and farming management of each cell in the mesh, covering 3.2% of the rice fields in Japan's Hokkaido region. We ran DNDC-Rice to simulate CH4 emissions under five simulated water regimes: the conventional water regime and four AWR scenarios with gradually increasing drainage. We found that AWR can reduce CH4 emission by up to 41% compared with the emission under conventional water regime. Including the changes in CO2 and nitrous oxide emissions, potential mitigation of greenhouse gas (GHG) was 2.6 Mg CO2 Eq. ha-1 yr-1. If this estimate is expanded to Japan's total rice fields, expected GHG mitigation is 4.3 Tg CO2 Eq. yr-1, which accounts for 0.32% of total GHG emissions from Japan. For a reliable national-scale assessment, however, databases on soil, weather, and farming management must be constructed at a national scale, as these factors are widely variable between regions in Japan. © 2009 Blackwell Publishing Ltd. Source

Saito T.,Fukushima Agricultural Technology Center | Saito T.,Tokyo University of Technology | Otani T.,Japan National Institute for Agro - Environmental Sciences | Seike N.,Japan National Institute for Agro - Environmental Sciences | Okazaki M.,Tokyo University of Technology
Soil Science and Plant Nutrition | Year: 2015

Dieldrin, an insecticide that is considered a persistent organic pollutant, remains in the soil for a long time after application. In recent years, dieldrin has been detected in cucumber (Cucumis sativus L.) fruits produced in some areas at concentrations exceeding the tolerance limit in Japan. Thus, we compared dieldrin residues in 19 vegetable crops produced in a dieldrin-contaminated field. Since dieldrin concentrations in the soil of each crop plot differed about 2-fold, we used the bioconcentration factor to compare the degree of dieldrin residue contamination among crops. The bioconcentration factors of Cucurbitaceae crops were much higher than those of non-Cucurbitaceae crops. Among non-Cucurbitaceae crops, the bioconcentration factors of komatsunas (Brassica campestris var. perviridis), Japanese radishes (Raphanus sativus L.), carrots (Dancus carota L.), and potatoes (Solanum tuberosum L.) were relatively high. In these Cucurbitaceae plants, dieldrin was not accumulated in particular parts or organs. On the other hand, in carrot roots, Japanese radish roots, and potato tubers, higher amounts of dieldrin were detected in the skin, small amounts were found in the outer flesh, and none was detected in the inner flesh, core, or leaf. To select the alternative crops to grow in dieldrin-contaminated fields, we propose to use the ‘‘tolerance limit over factor’’, which we calculated by dividing the bioconcentration factor by the tolerance limit of the crop. The tolerance limit over factor of Cucurbitaceae crops was higher than that of non-Cucurbitaceae crops. In Cucurbitaceae, the tolerance limit over factor of cucumbers was much higher than that of zucchini and pumpkins, though the bioconcentration factors of these cucurbits were nearly the same. In non-Cucurbitaceae crops, the tolerance limit over factors of komatsunas, Japanese radishes, and potatoes were similar in value to those of zucchini (Cucurbita pepo L.) and pumpkins (Cucurbita maxima Duch.). By considering the tolerance limit over factor values, we propose that Cucurbitaceae crops, root crops (especially Japanese radish), tubers (especially potato), and leafy vegetables (especially komatsuna), in which dieldrin tolerance limits are set at low concentrations, are not appropriate for cultivation in dieldrin-contaminated fields. © 2012 Japanese Society of Soil Science and Plant Nutrition. Source

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